A phase-shifting technique for full-field measurement of the strain of an object in electronic speckle-shearing interferometry is presented. The object under study is placed on a rotating platform and illuminated by an expanded laser beam. Its images are recorded at short intervals by a shearing CCD camera and stored directly into a computer. By subtracting the series of images from the first one, fringe patterns that represent the object surface strain can be obtained and shown on a computer monitor if the object is loaded. When the object is given a small angle of rotation, an additional phase will be introduced into the fringe patterns. Theoretical analysis shows that this additional phase is linear. Therefore, the electronic speckle shearing phase-shifting technique can be realized by rotating the test object. The small angle can be obtained exactly by a rotating platform controlled by a computer. The theory of the method and system as well as some experimental results is presented.
"Digital phase-shifting shearography for strain measurement by using a rotating platform system," Optical Engineering 44(8), 085601 (1 August 2005). https://doi.org/10.1117/1.2010127